Continuous directional water transport on the peristome surface of Nepenthes alata

• Published in: Nature (London) 2016-04, Vol.532 (7597), p.85-89
• Main Authors: Chen, Huawei, Zhang, Pengfei, Zhang, Liwen, Liu, Hongliang, Jiang, Ying, Zhang, Deyuan, Han, Zhiwu, Jiang, Lei
• Format: Article
• Language: English
• Subjects: 639/301/54; 639/638/542/967; 639/766/747; Animals; Biological Transport; Biomimetics; Botany; Caryophyllidae; Contact angle; Driving ability; Energy gradient; Flowers & plants; Humanities and Social Sciences; Insecta; letter; Magnoliopsida - anatomy & histology; Magnoliopsida - metabolism; multidisciplinary; Observations; Physiological aspects; Plant Epidermis - anatomy & histology; Plant Epidermis - metabolism; Plant-water relationships; Science; Surface Properties; Water - metabolism; Water flow; Water Movements; Water transport
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature17189

Insects are captured by the carnivorous plant Nepenthes alata when they ‘aquaplane’ on the wet rim, or ‘peristome’, of the plant’s pitcher organ; here it is shown that unidirectional water flow is crucial to the complete wetting of the peristome, and that the underlying mechanism involves multiscale structural features. Pitcher plants have a way with water The carnivorous plant Nepenthes alata captures insects when they 'aquaplane' on the wet rim, or peristome, of the plant's pitcher organ. Huawei Chen and colleagues show that this is achieved through continuous directional water transport on the peristome surface, a result of multi-scale structure features involving periodic duck-billed micro-cavities with arch-shaped open edges. These features optimize capillary rise in the transport direction and prevent back-flow by pinning in place any water front moving in the reverse direction. This produces unidirectional flow despite the absence of any gradient in surface energy, and much faster transport than previously observed with asymmetrically structured surfaces. The mechanisms underlying this behaviour could be relevant for artificial fluid-transport systems with practical applications. Numerous natural systems contain surfaces or threads that enable directional water transport 1 , 2 , 3 , 4 , 5 , 6 , 7 . This behaviour is usually ascribed to hierarchical structural features at the microscale and nanoscale, with gradients in surface energy 8 , 9 and gradients in Laplace pressure 10 thought to be the main driving forces. Here we study the prey-trapping pitcher organs of the carnivorous plant Nepenthes alata . We find that continuous, directional water transport occurs on the surface of the ‘peristome’—the rim of the pitcher—because of its multiscale structure, which optimizes and enhances capillary rise 11 , 12 in the transport direction, and prevents backflow by pinning in place any water front that is moving in the reverse direction. This results not only in unidirectional flow despite the absence of any surface-energy gradient, but also in a transport speed that is much higher than previously thought. We anticipate that the basic ‘design’ principles underlying this behaviour could be used to develop artificial fluid-transport systems with practical applications.